British Gas and BT have been singled out for failing on customer service, as research shows that utility company call centres have the worse track record for dealing with complaints.

A Citizens Advice Bureau survey found nearly a third of respondents spent more than half an hour on the phone to their utility companies trying to resolve problems with their services.

The vast majority (77%) of those completing a survey on the charity's website were unable to resolve their problems in just one call. Even though many utility companies provide cheap or freephone numbers, the report warned that those without a landline faced huge bills trying to get through on their mobile phones.

Advisers in the Citizens Advice Bureau's 77 offices in England and Wales face the same problems when trying to contact utility companies on behalf of clients, the report says. The charity estimates that bureaux could help up to 55,000 extra people a year if calls from advisers to utility companies lasted no more than 10 minutes.

A separate Ipsos Mori survey revealed that even though there had been some improvement since the last report in 2004 utility call centres are still the worst-performers. More than one in four customers (27%) who had contacted a utility company by telephone in the past 12 months were dissatisfied with the way in which their calls had been handled. This compared with 16% for those who had contacted a financial services company call centre and 17% for those who had contacted a retailer. Telephone and gas companies fared the worst.

The website survey found that nine out of 10 respondents (89%) were either dissatisfied or very dissatisfied with the way their last call to a landline provider had been handled. Eighty-seven per cent of the calls causing dissatisfaction were to BT, considerably more than BT's 68% market share. For those contacting a gas supplier, 81% of respondents were either dissatisfied or very dissatisfied - 71% of these were to British Gas, which has a 46% market share.

Citizens Advice says there are too few incentives for suppliers to improve their performance. It is calling on regulators to require fuel and telecoms suppliers to provide up-to-date information about customer satisfaction, as well as costs.

Citizens Advice chief executive David Harker said it was essential that customers were able to contact their utility suppliers when services broke down. "Utilities such as gas and telecoms are essential services that people need in order to survive in the modern world ... yet this report shows that many companies have a long way to go."

He called on heads of all utility supply companies, "especially British Telecom and British Gas", to improve services.

BT said it was "concerned" and would try to improve its customer care. A statement said that at the time of the survey the company had been experiencing teething problems with a new IT system.

British Gas said the company had invested more than £60m employing 800 more frontline agents and providing better training, and that customer service had improved. "The most recent figures from Energywatch show that our complaint levels have fallen by 82% since April."

Double trouble

· British Gas converted Sarah Perry in Kent to a regular meter, which the fitter failed to reset to zero. She was billed for £132 after three days. It took more than a year to fix the error.

· A Hampshire woman decided to disconnect one of her BT phone lines after her husband died. After three days she got through to the correct department - but both lines were cut off. It took eight days to get one reconnected. Source: Citizens Advice